Changes in cadmium and zinc phytoavailability in agricultural soil after amendment with papermill sludge and biosolids

The co-disposal of papermill sludge with biosolids is seen as an alternativ e soil amendment to papermill sludge and inorganic fertilizer. The objectiv es of this study were to assess the suitability of co-disposal of papermill sludge and biosolids by measuring changes in the soil physicochemical prop erties and the phytoavailability of cadmium (Cd) and zinc (Zn). Biosolids w ere applied with papermill sludge as an alternative source of N to inorgani c fertilizers at rates calculated on the basis of C:N ratios of the amendme nts and common papermill sludge disposal practices. Perennial ryegrass (Lol ium perenne L.) was grown on amended soils for 6 months under glasshouse co nditions. The papermill sludge amendment alone increased soil pH and the ra te of carbon degradation compared to the control (no amendment) and biosoli d co-disposal amendment. There was no difference in dry matter yield per po t of ryegrass between the treatments. Cadmium concentrations in plant tissu e increased through the trial with the application of biosolids and papermi ll sludge. These findings were correlated well with the sorption properties of the soils for Cd as derived from isotherms. However, Zn uptake was unaf fected by the application of the papermill sludge and biosolids.